Zig-zag folding has been utilized in the paper field since before the turn of the century. Although there are many forms of zig-zag folding apparatus, two general types emerge -- one in which the tuckers cooperate with mechanically controlled grippers and the second wherein the grippers are not mechanically controlled. Representative of the first type is Lewis U.S. Pat. No. 1,109,296 and my U.S. Pat. No. 3,195,882. Representative of the second is Wyrick U.S. Pat. No. 2,246,336 and DeLigt U.S. Pat. No. 3,784,188. This invention has to do with the second type.
The zig-zag folder employing mechanically actuated grippers gives more precise control over the position of the fold but at the expense of much more complicated equipment and unsatisfactory noise levels. On the other hand, the second type seemingly would avoid both of these drawbacks, but without the utilization of the instant invention, I found that it was not possible to reliably obtain reproducibility of folding at the precise positions desired independent of speed. In particular, there is no satisfactory arrangement for operating at web speeds of the order of 1,000 feet per minute. In the case of the mechanically controlled grippers, the noise level is quite high, while in the uncontrolled gripper type, the high speed cannot be maintained reliably -- i.e., folding at predetermined locations.
It will be appreciated that precision in locating the line of fold is most desirable. For example, in business forms which are transversely perforated to permit separation of one panel or set from another after printing in a computer or the like, it is essential that the zig-zag folding occur precisely at the lines of perforation. Further, even where there is no transverse perforation, it is still desirable (as in the case of facial tissues) to have the transverse folds at precisely equally spaced apart distances to develop a rectangular stack.
These objectives have been realized by the instant invention. The basic folding apparatus is of the simplest arrangement, i.e., providing the folding and release functions within a triangular area which is essentially equilateral. The tuckers and grippers are arranged for travel in loops having portions defining the aforementioned essentially equilateral triangle -- in the illustrated embodiment, the loops are adjacent at the point of tucker-web engagement and then diverge. By providing a controlled surplus of said web above the point of folding and releasing the surplus simultaneously with the folding, I have achieved the desired precision in folding. Although surplus web or slack has been provided previously, as in the aforementioned Wyrick patent, it has not been provided between means for continuously and uniformly advancing the web and retarding means so that the surplus is withheld until the time of tucker web engagement. The slack is then used up by the actual tucking operation and also by the faster travel of the grippers going around the arcuate portion of the loop.